Regulating device



-MflrCh 11, 1941. w VANCE REGULATING DEVICE 2 Sheets-Sheet 1 OriginalFiled Oct. 51, 1955 HIS HTTOFINE Y INVENTOR ArthurWVance -March1l,1941.NC Re. 21,749

REGULATING- DEVICE I Original Filed Oct. 31, 1933 2- Sheets-Sheet 2-=I.I I I I I I I I*- INVENTOR I ArthdrWT/lpnce Mm BY 33 HIS HTTOHNE YReiuuedMarrll, 1941 UNITED STATES momma nnvron Arthur w. Vance,Haddonfleld, N. 1., alaignor to Radio Corporation of America, acorporation of Delaware Original No. 2,075,966, dated April 6, 1037,Serial No. 696,001, October 31,1933. Application for reissue December22, 1938, Serial No. 247,305

24 Claims.

My invention relates to regulating devices and particularly to lowimpedance voltage regulating and current regulating circuits whichutilize electric discharge tubes for maintaining either a constantvoltage or a constant current output.

There are many applications for a high voltage source which has a lowimpedance and a more constant voltage output than can be obtained from arectifier and filter system. As an example,

television amplifiers cannot be supplied with volt age from a filtersystem with satisfactory results,

Previously, in cases where the voltage requirements have been so strict,it has been necessary to employ batteries made up of a large number 16of cells. Such batteries are expensive and must be replacedperiodically.

There are also many applications for a low impedance source whichsupplies a constant current regardless of adverse conditions such as g9varying load impedance or varying line voltage.

It is, accordingly, an object of my invention to provide a regulatingcircuit which will hold the voltage across a load constant when thevoltage is supplied from a source of varying voltage such 25 as a sourceof rectified current.

A further object of my invention is to provide an improved currentregulating circuit which will supply a constant current to a load.

A still further object of my invention is to 30 provide voltage andcurrent regulating circuits of the above-mentioned types which do nothave any batteries therein.

In practicing certain embodiments of my in vention, I connect a powertube in series with u the load, and vary the impedance ofthe power tubein accordance with voltage'changes by connecting the control grid of thepower tube to the output circuit of a direct current amplifier, theinput circuit of the direct current amplifier being 40 connected to aresistor shunted across the load. In certain specific embodiments, allbatteries,

such as grid biasing batteries, are eliminated by utilizing a glow tubein one of two voltage-opposing circuits.

45 In practicing other embodiments of my invention, a power tube isconnected in shunt to the load instead of in series therewithj Also, incertain embodiments, a resistor is connected in series with the load,instead of in shunt to it,

so for applying a regulating voltage to the grid of the power tube.

Other features and advantages of my invention will appear from thefollowing description taken. in connection with the accompanying adrawings, in which Figure 1 is a. circuit diagram of a voltageregulating system constructed in accordance with one embodiment of myinvention; v

Fig. 2 is a circuit diagram of the voltage regulator which, inaccordance with my invention, 5 does not require the use of batteries;

Fig. 3 is a circuit diagram of a voltage regulator constructed inaccordance with another embodiment of my invention; and

Fig. 4 is a circuit diagram of a current regulal0 tor constructed inaccordance with one embodiment of m invention.

Referring to Fig. 1, a load is supplied with direct current from a fullwave rectifier 01' conventional design. The rectifier i comprises recl5tifier tubes 3 and 5 having hot cathodes l and 3, respectively, whichare supplied with current from the filament secondary winding l i of asupply transformer iii. The anodes l5 and ll of the rectifier tubes 3and. 5, respectively, are connected to the ends of the high potentialwinding 13 .of the transformer i3.

' A conductor 2| leading from the mid-point of the secondary winding I9,which forms one output lead or terminal of the rectifier I, is groundedand connected to the bottom terminal of the load 23.

The other output lead or terminal 25 of the rectifier i is connected tothe upper terminal of the load 23 through a filter choke 21 and a powertube 29. This connection may be traced from the rectifier i through thechoke coil 2'! to the plate 3| of the power tube 29, through thespacecurrent path in the tube to the filament 33 and through thefilament shunting resistor 35 and 35 the conductor 31 to the upperterminal of the load 23.

The usual filter condenser 39 is connected be-. tween the load end ofthe choke coil 21 and ground. It will be apparent that the voltagesupplied to the load 23 would have a fairly large hum component it onlythe choke coil 2'! and condenser 39 were relied on to filter therectifier output. Therefore, in accordance with my invention, I providea direct current amplifier I so connected in the circuit that the plateimpedance of the power tube 29 is varied in the proper manner tomaintain the voltage across the load constant.

The direct current amplifier 6! comprises an electric discharge device43 which, preferably, is a screen grid vacuum tube, and another electricdischarge device 45 which functions as a plate impedance for the firstmentioned device 43. In

accordance with a specific feature 0! my invention, the control voltageto the input circuit of the direct current amplifier 4| is supplied froma resistor 41 connected in shunt to the load II.

Obviously, in order to obtain maximum-control, the grid 49 and cathodell of the vacuum tube 43 should be connected across the entire resistor41 to apply the total voltage drop of the resistor 41 to the amplifierinput circuit. Such a connection, however, would require a very largebiasing battery in a system where there is a voltage drop of severalhundred volts across the load. Furthermore, a direct current connectionacross the entire resistor 41 is not necessary in order to obtain thenecessary control ior variations in the voltage. v

I obtain the proper control tor the above-mentioned voltage variationsand a certain amount of control for the higher frequency or humvariations by conductively connecting the grid 40 and the cathode 5|across a small section of the resistor 41, thus allowing the utilization01' a comparatively small biasing battery I in the grid circuit.

y The desired additional regulating action for eliminating hum orcomparatively high frequency voltage variations is obtained byconnecting the control grid 49 and the cathode ll across the entireresistor 41 by means oi coupling condensers 55 and 51, respectively.

, The screen grid 58 of the vacuum tube 43 is supplied with the properpositive potential by connecting it to a point on the resistor 41.

The plate iii of the vacuum tube 43 is connected through the vacuum tube45, which serves as a coupling resistor to the upper or positiveterminal of the resistor 41. This circuit may be traced from the plateii oi the amplifier tube 43 through a resistor ll to the cathode II ofthe coupling tube 45, through the space charge path of the tube to theanode B1, and through themductors 69 and 31 to thepositive terminal ofthe resistor 41.

The screen grid 1| of tube 45 is supplied with a suitable positivepotential by means of a battery'13.

The contro1 grid 15 of coupling tube 4! is connected to the upperterminal of the resistor 03 so that the plate impedance of the couplingtube changes with a change in current through the resistor 63. It willbe seen that the current flow through the resistor "is in such adirection that it the current flow increases. the grid 1! is made morenegative and the plate impedance of the coupling tube 45 increases.

v The plate impedance of the power tube 2! is controlled in accordancewith the output or the direct current amplifier 4| by means of the powertube control grid 11 which is connected by means of a conductor 19 tothe plate ll or the amplifier tube 43.

The above described circuit provides what may be referred to as negativeregeneration, since the direct current amplifier 41 is connected toresist variations in voltage rather than to amplify them. This actionwill be understood by considerlng the action of the amplifier 41 whenthe voltage output of the rectifier I increases. Such an increase willcause an increase in current fiow through the shunting resistor 41 andmake the control grid 48 of the amplifier tube 48 more positive withrespect to the cathode II. This causes an increase in current throughthe resistor it and coupling tube 45, whereby the plate ll becomes lesspositive.

Since the control grid 11 of the power tube II is connected to the plateII, it also becomes less positive, that is, more negative, and theimpedance of the power tube 28 is increased, whereby any increase involtage drop across the shunting resistor 41 is opposed. It will beunderstood that the voltage variation across the load 28 which ispermitted by the system is a function of the gain of the direct currentamplifier 4|, the voltage variation being decreased by increasing thegain 0! the amplifier.

I! desired, the coupling tube 45 may be replaced by an ordinary couplingimpedance, but the gain of the amplifier 4| is increased by employingthe coupling tube 45 since the coupling tube impedance increases with anincrease in the plate current of tube 43. Also, a screen grid tube witha high negative bias on the grid and a low positive voltage on theplate, as in the case of tube 45, has a very high plate impedance, 0!the order of several megohms, yet the direct current drop across thetube is only a few volts with a plate current 0! cheer two milliamperes.resistor of similar impedance would have a very high voltage drop at thesame current and it would be diflicult and expensive to supply thenecessary high voltage. I

Although in the circuit shown in Fig. 1 there is very'little drain onthe batteries, obviously,

the elimination of all batteries is desirable.

Fig. 2 shows a system in which batteries have been eliminated byutilizing a special glow tube circuit. In Figs. 1 and 2 like parts areindicated by like reference numerals. It will be noted that in Fig. 2the choke coil 21 of the filter has been omitted, this being feasiblewhen the direct current amplifier or the regulator systemhas a highgain.

In Fig. 2 the direct current amplifier 81 comprises two screen gridtubes and 85. As in Fig. 1, the control voltage for the direct currentamplifier II is provided by means or a resistor 81 connected in shunt tothe load 23.

A portion of the resistor 81 is shunted by a glow tube I! connected inseries with a current limiting resistor I. The glow tube may be any oneof the well known types such as a neon lamp. The control grid 83 or theamplifier tube 83 is connected to a point on that portion 01 theresister 81 which is shunted by the glow tube 89, while the cathode isconnected to a point between the glow tube 88 and the current limitingresistor ll.

The glow tube It will have a substantially constant voltage dropthereacross so that it supplies a substantially constant biasing voltagein the grid circuit. It will be noted that since the resister 81 and theglow tube 89 are connected in parallel with respect to the rectifier,their voltage drops arein opposition in the grid circuit of theamplifier tube 83.

In one embodiment of my invention, where the voltage drop across theload 23 was 230 volts, the glow tube II had a constant voltage drop orvolts thereacross. while the portion of the resistor between the points82 and 94 had a normal voltage drop of 113 volts thereacross. Thissupplied the control grid 83 with a negative bias or 3 volts.

The plate 1 of the amplifier tube 83 is connected to the positiveterminals of the voltage supply and load through a high resistance unitII. The plate 01 is conductively coupled to the control gridlll of thetube 85. In order to maintain the control grid lli negative with respectto the cathode Ill or tube II, the cathode I08 60 a sistor 41 by meansof the coupling condensers is connected to a point on a resistor I99connected in shunt to the load, which point is positive with respect tothe plate 91 and grid I9 I The plate I91 of the tube 99 is connected tothe positive terminals of the voltage supply and load through a resistorI99-which may be of the same value asthe resistor 99 in the platecircuit of the other tube. In one embodiment of the invention, resistors99 and I99 had a value of l megohm.

Obviously, the plate I91 of tube 99 must be at a higher potential thanthe plate 91 of tube 99 in order that it shall be at a positivevaluewith respect to its cathode I99. It is maintained at this higherpotential since the plate current of the tube 99 is less than the platecurrent of the tube 89 due to the control grid Ill of tube 99 alwaysbeing maintained more negative than the control grid 99 of tube 99.

The screen grid III of tube 99 is supplied with a suitable positivepotential by means of a resistor 9 connected in shunt to the load 99,while the screen grid I ll of the tube 99 is supplied with the properpotential. by connecting it to the positive terminal of the power supplythrough a conductor I I1.

As in Fig. 1, the input circuit of the direct current amplifier 9| hasan alternating current connection across the entire resistor 91, thisconnection being through coupling condensers H9 and I2 I. A strongcontrol voltage will be applied to the amplifier input circuit throughthe coupling condensers for reducing voltage variations of acomparatively high frequency such as those having a frequency of 60 or120 cycles.

In Fig. 3, the circuit of Fig. 1 is shown modified for utilizing avoltage control tube connected in shunt to the load instead of in serieswith it. In the two figures like parts are indicated by like referencenumerals.

Referring to Fig. 3, the power tube is shown replaced by a smaller threeelement tube I29 connected in shunt to the load. It will be seen thatthe tube I29 acts as a bleeder resistor, the impedance of which may bevaried by means of a control electrode I29.

With the valtage control tube I29 in shunt to the load, the phase of thecontrol voltage applied to the control grid I29 must be such that anincrease in voltage drop across the resistor 41 causes a decrease in theplate impedance of the tube I29.

In order to get the proper phase relation, the control grid 49 of theamplifier tube 49 is connected below the point I21 on the resistor 41 towhich the cathode II is connected. Since this connection would put thecontrol grid 49 at a high negative potential, a biasing battery I 29 isinserted in the grid circuit for maintaining the grid 49 at the propernegative bias. The grid 49 and cathode ii are coupled across the entirere- I9I and I93, respectively, as in l ig. 1.

The impedance of the voltage control tube I29 is controlled inaccordance with the output of the direct current amplifier 4i by meansof the control grid I29 which is conductively coupled to the plate 9i ofthe amplifier tube 49. In order to maintain the control grid I29 at anegative potential with respect to the cathode I99, a biasing batteryi91 is inserted in the connecting lead between the plate 9i and thecontrol grid I29.

All of the above described circuits have the common features of aresistor connected in shunt to the load for supplying the controlvolts-so to the direct current amplifier. They also have the commonfeature of a direct current amplifier which has its input circuitconductively connected across only a part of the voltage controltosistor for opposing slow voltage changes and capacitively connectedacross the entire voltage control resistor ior opposing voltage humvariations.

Referring to Fig. 4, where parts similar to those in Fig. 2 areindicated by like reference numerals, there is shown a current limitingsystem which does not require the use of batteries. As in Figs. 1 and 2.a power tube 99 is connected in series with thesource of rectifyingcurrent and the load. In this circuit, however, the control voltage issupplied from a resistor I99 connected in series with theload.

The control voltage is applied to the input of a direct currentamplifier II which is similar to the one shown in Figure 2.

The main distinction between the circuits Figs. 2 and 4 resides in theinput circuit of the direct current amplifier 9i. The cathode 99 of thefirst amplifier tube 99 is connected to a point on the series resistorI99, while the control grid 99 of the amplifier tube 99 is connectedthrough a conductor I to a circuit in shunt to the rectifier. This shuntcircuit comprises a grid glow tube I49 connected in series with acurrent limiting resistor I49.

With respectto the grid circuit of the amplifier tube99, the glow tubeI49 is connected in series relation with the portion of the seriesresistor I99 which is in the said arid circuit. With respect to therectifier, however, the glow tube I49 and the series control resistorI99 are connected in parallel. drops across the glow tube I49 and theresistor I99 are in series opposition in the amplifier grid circuit sothat thedesired small negative bias is applied to the control grid 99.

It will be noted that the glow tube I49 and the resistor I41, whichsupplies the desired potential to the screen grid III and the cathodeI99, are connected across the power supply at a point between therectifier i and the power tube 29 instead of at a point between the load29 and the power tube 29 as in the preceding figures. This is desirablesince the voltage across tggoad may be varied greatly in maintainingcurrent through it substantially constant.

In both Fig. 2 and Fig. 4 the glow tube and current limiting resistormay be replaced by a ballast lamp connected in series with a resistor.Since a ballastlamp is a constant current device, the drop across theresistor will be substantially constant and may be utilized in place ofthe voltage drop across a glow tube. While it is preferred that a glowtube or some other device which has a substantially constant voltagedrop thereacross be used, the operation of the circuit will besatisfactory so long as the voltage variation across the glow tube orsubstituted device is small compared with the voltage variation acrossthe resistor. It will be noted that both the glow tube and the ballastlamp have an impedance which varies with the voltage impressed acrossthem.

From the foregoing description, it will be apparent that I have providedregulating systems which are highly effective in supplying a load witheither a constant voltage or a constant current and which are economicaland convenient to operate. More particularly, I have provided cer-' tainvacuum tube regulating systems which derive all the voltages for thevacuum tubes from the It will be apparent that the voltage' source ofpower to be regulated whereby all batteries are eliminated. Also, I haveprovided certain other vacuum tube regulating systems which require onlysmall biasing batteries which will havea long life.

Various modifications may. be made in my invention without departingfrom the spirit and scope thereof, and I desire, therefore, that onlysuch limitations shall be placed thereon as are necessitated by the pior art and set forth in the appended claims.

I claim as my'invention:

i, In a voltage regulating system for a source of variable voltage, aload, a voltage divider resistor shunted across said load, an electricdis- I charge tube having a control electrode, said tube being connectedin the circuit between said source and said voltage divider resistor,and means for controlling ,the impedance of said tube in accori iancewith changes in voltage drop across said voltage divider resistor, saidmeans comprising a direct current amplifier having an input circuitconnected to said voltage divider resistor and an output circuitconnected to said control electrode.

2. A system according to claim 1 characterized in that a second circuitincluding a glow tube is connected in shunt to a portion oi, saidvoltage divider resistor, said glow tube and said portion beingconnected in series relation in said input circuit 01' the directcurrent amplifier.

3. In a voltage regulating system for a source of variable voltage,- aload, a voltage divider resistor shunted across said load, an electricdischarge tube connected in series with said source and said load, saidtube having a control electrode, and'means for. increasing the impedanceof said tube in responseto an increase in current through said voltagedivider resistor, said means including a direct current amplifier havingits i input circuit'connected across a low potential portioii of saidvoltage divider resistor and its output circuit connected to saidcontrol grid.

14'. In combination, an amplifier comprising an electric dischargedevice having input electrodes including a control electrode, a sourceof potential, a constant impedance device connected in series with saidsource, a gaseous discharge device also connected in series with saidsource, and means for connecting said impedance device and said gaseousdischarge device in series relation between said input electrodes withthe voltage in said devices in opposition.

Q5. Apparatus according to claim 4 characterized in that the gaseousdischarge device is connected in a circuit which is in shunt to theconstant impedance device.

6. Apparatus according to claim 4 characterized in that the gaseousdischarge device is a glow tube.

7. In combination, an amplifier comprising an electric discharge devicehaving input electrodes including a control electrode, a source ofpotential, a variable impedance circuit connected in series .with saidsource of potential, a portion of said circuit having a constant voltagedrop thereacross, an impedance device of comparatively constantimpedance connected in a circuit in shunt to said variable impedancecircuit, and means for connecting saidimpedance device and a portion ofsaid variable .impedance circuit in series relation between said inputelectrodes.

8. In combination, a source of electrical energy, a load connectedthereto, an electric discharge tube connected in series with said load,a direct-current amplifier having input electrodes and an outputcircuit, a resistor connected across said load, a circuit including aglow tube connected across at least a portion of said resistor, one ofsaid input electrodes being connected to the portion of said resistorshunted by said glow tube-and the other of said input electrodes beingconnected to said glow tube circuit, and means for so connecting theoutput circuit of said amplifier to said electric discharge tube thatthe impedance of said tube is increased in response to an increase inthe voltage of said source.

9. In a voltage regulating system for a source of variable voltage, aload, an impedance device shunted across said load, an electricdischarge tube connected in series with said source and said load, saidtube having a control electrode, and means for increasing the impedanceof said tube in response to an increase in current through .saidimpedance device, said means including a direct current amplifier havinginput electrodes and an output'circuit, a circuit including a glow tubeconnected across at least a portion of said impedance device, one ofsaid input electrodes being connected to the portion of said impedancedevice shunted by said glow tube and the other oi said input electrodesbeing connected to said glow tube circuit, said output circuit beingconnected to said control grid.

10. In a voltage regulating system including a source of variablevoltage and a load connected thereacross, an impedance unit connected inshunt to said source, a variable impedance device connected in thecircuit between said source and said impedance unit, and means includinga direct current amplifier for controlling the impedance of said devicein accordance with variations in voltage supplied from said source, saidamplifier having input electrodes conductively, connected across aportion 0! said impedance unit, said input-electrodes also being coupledacross a larger portion 01 said impedance unit by coupling means whichwill pass pulsating voltages only.

11. In a voltage regulating system including a source of variablevoltage and a load connected thereacross, an impedance unit connected inshunt to said source, a variable impedance device connected in thecircuit between said source and said impedance unit, means including a'directcurrent amplifier for controlling the impedance of said device inaccordance with variations in voltage supplied from said source, saidamplifier having input electrodes and an output circuit, means forconductively connecting said input electrodes across a portion of saidimpedance unit, means for capacitatively connecting said inputelectrodes across a larger portion of said impedance unit, and means forcoupling the output circuit of said amplifier to said variable impedancedevice.

12. In a current regulating system, a source of current, a loadconnected thereto, an electric discharge tube connected in series withsaid load, a resistor also connected in series with said load, aglow-tube circuit connected across said source and in shunt relation toat least a portion of said resistor, and means for increasing theimpedance of said tube in response to an increase in current throughsaid resistor, said means including a direct current amplifier having aninput circuit connected across said glow tube and said portion of saidresistor, said glow tube and said resistor portion being in seriesrelation with respect to said input circuit.

13. In combination, a source of voltage, an amplifier having an inputcircuit including input electrodes, a substantially constant impedancedevice connected across said source, a gaseous discharge deviceconnected in parallel with said constant impedance device, means forconnecting one of said input electrodes to said constant impedancedevice, and means for connecting the other of said input electrodes tosaid gaseous discharge device whereby said constant impedance device andsaid gaseous discharge device are connected in series in said inputcircuit.

14. In combination, an amplifier comprising an electric discharge tubehaving input electrodes including a control electrode, a source ofpotential, a first impedance device connected in series with saidsource, said first device having a substantially constant impedance, asecond impedance device also connected in series with said source, saidsecond device having an impedance which changes substantiallyinstantaneously in response to a change in voltage impressedthereacross, and means for connecting said impedance devices in seriesrelation between said input electrodes with the voltage drops in saiddevices in opposition.

5 15. A voltage regulating device including a source of current having apair of terminals, a tube including electrodes and a grid, a conductiveconnection between one of said terminals and one of said electrodes, aconnection leading from the otherelectrode, out-put means for the deviceconnected at one side to the last mentioned connection, a connectionleading from the remaining terminal of the source of current, controlmeans for said grid bridged between the last 35 two connections, and aconductive connection between said grid and the controlling means, saidcontrolling means including a discharge gap and a resistor in serieswith the discharge gap and a contact movable over said resistor andforming a terminal for the last mentioned connection.

16. A regulating circuit for direct currents, said circuit having aninput and an output tending to very from normal in accordance with thepotential diilerence between the output and input, said 45 circuitincluding a variable resistance tube,

means for supplying a constant potential, and

means to regulate the resistance of the tube in conformity withvariations from normal of the potential difierence between the firstmeans and 5 the output.

17. A voltage regulating device including a source of current havingapair of terminals, a tube including electrodes and a grid, a conductiveconnection between one of said terminals 55 and one 01' said electrodes,a connection leading from the other electrode, out-put means for thedevice connected at one side to the last mentioned connection, aconnection leading from the remaining terminal 01' the source ofcurrent, control means for said grid bridged between the last twoconnections, and a conductive connection between said grid and thecontrolling means, said controlling means including a discharge gap anda resistor in series with the discharge gap and M a contact in serieswith said resistor and forming a terminal for the last mentionedconnection.

18. The invention as set forth in claim 16, .wherein said constantpotential means includes a gaseous discharge device.

18. The invention as set forth in claim 18, wherein said constantpotential means comprises a glow tube connected in series with aresistor.

20. The invention as set forth in claim 18,

wherein said regulating means comprises a voltage divider networkconnected across said output circuit.

21. A voltage regulating device including a source of current having apair of terminals, 8. tube including electrodes and a grid, a conductiveconnection between one 01' said terminals and one of said electrodes, aconnection leading from the other electrode, output means for the deviceconnected at one side to the last mentioned connection, a connectionleading from the remaining terminal of the source of current, controlmeans for said grid bridged between the last two connections, and adirect voltage responsive connection between said gridand thecontrolling means, said controlling means including a discharge gap anda resistor in series with the discharge gap and a contact movable oversaid resistor and forming a terminal for the last mentioned connection.

22. A voltage regulating device including a source of current having apair of terminals, a tube including electrodes and a grid, a conductiveconnection between one of said terminals and one of said electrodes, aconnection leading from the other electrode, output means for the deviceconnected at one side to the last mentioned connection, a connectionleading from the remaining terminal of the source of current, controlmeans for said grid bridged between the last two connections, and adirect voltage responsive connection between said grid and thecontrolling means, said controlling means including a discharge gap anda resistor in series with the discharge gap and a contact in series withsaidresistor and forming a terminal for the last mentioned connection.

23. A voltage regulating device includinga source of current having apair of terminals, a tube including-electrodes and a grid, a conductiveconnection between one of said terminals and one of said electrodes, aconnection leading from the other electrode, output means for the deviceconnected at one side to the last mentioned connection, a connectionleading from the remaining terminal of the source of current, controlmeans for said grid bridged between the last two connections, and adirect voltage responsive connection between said'grid and thecontrolling means, said controlling means including a discharge gap anda resistor in circuit with the discharge gap and a contact movable oversaid resistor and forming a terminal for the last mentioned connection.

24. A voltage regulating device including a source of currenthaving apair of terminals, a tube including electrodes and a grid, a conductiveconnection between one of said terminals and one of said electrodes, aconnection leading from the other electrode, output means for the deviceconnected at one side to the last mentioned connection, a connectionleading from the remaining terminal oi the source oi current, controlmeans for said grid bridged between the last two connections, and adirect voltage responsive connection between said grid and thecontrolling means, said controlling means including a discharge gap anda resistor in circuit with the discharge gap and a contact. in circuitwith said resistor and forming a terminal for the last mentionedconnection.

ARTHUR W. VANCE.

